Conventionally, there is known an ignition technology for causing volume ignition of air fuel mixture by plasma in a combustion chamber of an internal combustion engine. For example, Patent Document 1 discloses an internal combustion engine to which a technology of this kind is applied.
More particularly, in the internal combustion engine of Patent Document 1, a spark discharge is generated in a discharge gap of a spark plug, and a microwave is radiated toward the discharge gap. The microwave pulses supply energy to plasma generated at the discharge gap. As a result thereof, electrons in the plasma region are accelerated, the plasma expands, and air fuel mixture is ignited in volume.